Alexander S. Shumovsky

Simple test for hidden variables in spin-1 systems.

We resolve an old problem about the existence of hidden parameters in a three-dimensional quantum system by constructing an appropriate Bells type inequality. This reveals the nonclassical nature of most spin-1 states. We shortly discuss some physical implications and an underlying cause of this nonclassical behavior, as well as a perspective of its experimental verification.

Steady-state entanglement of two atoms created by classical driving field

The stabilization of entanglement caused by action of a classical driving field in the system of two-level atoms with the dipole interaction accompanied by spontaneous emission is discussed. An exact solution shows that the maximum amount of concurrence that can be achieved in the Lamb-Dicke limit is 0.43. Dependence of entanglement on interatomic distance and the classical driving field, beyond the Lamb-Dicke limit, is examined numerically.

Persistent entanglement in three-level atomic systems

We discuss the evolution towards persistent entangled state in an atom–photon system. A maximally entangled state can be stabilized at a local minimum of the system by draining some energy, thus obtaining a persistent entangled state. This scheme can be realized in three-level, Λ type atomic systems since the third level is a meta-stable state. In particular, we compare dynamical description based on the exact and effective models. Some experimental realizations are discussed.

Maximum entanglement and its proper measure

We discuss a definition of maximally entangled states in terms of maximum uncertainty of corresponding measurements. We describe a method of construction of bases of maximally entangled states. The entangled states that can be obtained from the maximally entangled states by means of SLOCC (stochastic local operations assisted by classical communications) we consider as semistable vectors. We discuss a measure of entanglement expressed in terms of a geometric invariant.

Entanglement and the SU(2) phase states in atomic systems

We show that a system of 2n identical two-level atoms interacting with n cavity photons manifests entanglement and that the set of entangled states coincides with the so-called SU(2) phase states. In particular, violationof classical realism in terms of the Greenberger-Horne-Zeilinger and Clauser-Horne-Shimoni-Holt conditions is proved. We discuss a property of entanglement expressed in terms of local measurements. We also show that generation of entangled states in the atom-photon systems under consideration strongly depends on the choice of initial conditions and that the parasitic influence of cavity detuning can be compensated through the use of Kerr medium.

Aharonov-Bohm effect induced by light in a fiber

A weakly coupled normal‐metal ring surrounding an optical fiber is considered under the condition that the frequency of light in fiber is larger than the conduction bandwidth of the metal. It is shown that in the presence of static magnetic field parallel to the fiber axis, the resistance of the ring is a nonmonotone function of the optical intensity and an oscillating function of the static magnetic flux with period equal to flux quantum hc/e. The temperature dependence of oscillations requires that inelastic mean free path of electrons is larger than the ring size, and does not relate to the energy level spacing to temperature ratio.

Robust entanglement in atomic systems via Λ -type processes

It is shown that the system of two three-level atoms in the {lambda} configuration in a cavity can evolve into a long-lived maximum entangled state if the Stokes photons vanish from the cavity by means of either leakage or damping. The difference in the evolution picture corresponding to the general model and effective model with two-photon process in a two-level system is discussed.

Entanglement, local measurements and symmetry

A definition of entanglement in terms of local measurements is discussed. Namely, the maximum entanglement corresponds to the states that cause the highest level of quantum fluctuations in all local measurements determined by the dynamic symmetry group of the system. A number of examples illustrating this definition is considered.

Dual representation of dipole photons

The quantum polarization and phase properties of an electric dipole radiation are examined. It is shown that, unlike the classical picture, the quantum description of polarization needs nine independent Stokes operators, forming a representation of SU(3) sub-algebra in the Weyl-Heisenberg algebra of photons. A corresponding Cartan algebra determines the cosine and sine of the radiation phase operators. A new representation of dipole photons is proposed. The generators of the Cartan algebra are diagonal in this representation so that the corresponding number states describe the number of photons with given radiation phase. The eigenstates of the radiation phase are determined. They have a discrete spectrum and natural behaviour in the classical limit. The relation between the radiation phase, operational phases and the Pegg-Barnett approach is discussed.

Stokes operators, angular momentum and radiation phase

We present a development of a method determining the quantum phase of radiation via the conservation of the angular momentum. It is shown that a set of generalized Stokes operators can be obtained with the aid of integrals of motion and two of them determine the radiation cosine and sine of the phase which corresponds to the azimuthal phase of the angular momentum according to the construction. We compare the evolution of the radiation cosine and sine and that for the conventional phase difference in the Jaynes-Cummings model. Although the expectation values coincide in some important cases, there is a striking difference between the behaviours of variances.